点击拖动，让物体旋转

using UnityEngine;
using System.Collections;

public class DragDays : MonoBehaviour {

    Ray ray;
    public GameObject days;
    void Start () {
        xMoon = camera.WorldToScreenPoint(moon.transform.position).x;
        yMoon = camera.WorldToScreenPoint(moon.transform.position).y;
        x = days.transform.eulerAngles.x;
        y = days.transform.eulerAngles.y;
        z = days.transform.eulerAngles.z;
    }
    public GameObject moon;
    //转盘的欧拉角
    float x;
    float y;
    float z;
    //鼠标的位置
    float xScreen;
    float yScreen;
    //月亮的位置
    float xMoon;
    float yMoon;
    void Update () {
       
    if(Input.GetMouseButton(0))
    {
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        RaycastHit hit;
        if(Physics.Raycast(ray,out hit))
        {
            if (hit.transform==days.transform)
            {
                xScreen = Input.mousePosition.x;
                yScreen = Input.mousePosition.y;
                //分别考虑四个象限
                //第一象限
                if(xScreen>xMoon&&yScreen>yMoon)
                {
                        y = y + Input.GetAxis("Mouse X") - Input.GetAxis("Mouse Y");
                }//第四象限
                else if(xScreen>xMoon&&yScreen<yMoon)
                {
                        y = y - Input.GetAxis("Mouse X") - Input.GetAxis("Mouse Y");
                }//第三象限
                else if(xScreen<xMoon&&yScreen<yMoon)
                {
                        y = y - Input.GetAxis("Mouse X") + Input.GetAxis("Mouse Y");
                }//第二象限
                else
                {
                        y = y + Input.GetAxis("Mouse X") + Input.GetAxis("Mouse Y");
                }
                xScreen = Input.mousePosition.x;
                yScreen = Input.mousePosition.y;
            }
            days.transform.eulerAngles = new Vector3(x, y, z);
        }
    }
    }
}